If it is the square key with the black resistor it most likely isn't the key. Most of the time one of the little tiny wires that go into the ign lock cylinder break and you need to replace the cylinder. There are 10 different possible keys. I know some people who just buy a lock cylinder and plug it in under the dash and leave the key in it. Or I worked with a guy who figured the resistance value for all ten keys and he would just go to radio shack and buy resistors and sodar them into the column harness bypassing the lock cylinder all together.
04 Yukon XL 2500 4x4 8.1
91 K-1500 5.7 RV cam 700-R4 stage 2 shift kit
08 Cadillac SRX 3.6 AWD box stock
49 *****'* CJ3A Jeep
There is no replacement for displacement!